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SA man poisoned by someone 'very close'

Those people closest to an Adelaide man who was fatally poisoned in 2015, including his then partner, are the focus of an investigation into his murder.

Police now believe 63-year-old David Lawrence, who died in his Morphett Vale home in December 2015, was deliberately poisoned through lethal doses of prescription medications added to his food and drinks.

Mr Lawrence had lived for about 18 months with his partner before his death. She has since moved to Dapto, near Wollongong in NSW.

Detective Superintendent Des Bray says her home was raided last month, with several people interviewed and various items seized during the search.

He says police believe Mr Lawrence's killer was likely "very close" to him, but that does not necessarily mean it was his then partner.

"The focus of our investigation will be those closest to him, those involved in changing his will and the beneficiaries of his will," he told reporters on Friday.

"Aside from that we will keep an open mind and explore every possibility."

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Det Supt Bray said Mr Lawrence was a healthy man with only minor health conditions and his death was unexplained until a toxicology report showed there were seven prescription medications in his body when he died.

Only two of the drugs were his, and two of the other five were found in lethal levels.

Mr Lawrence's will was changed in the weeks leading up to his death, and his estate was "worth somebody killing somebody for", Det Supt Bray said.

He said the man's siblings are not being looked as part of the investigation.

Police are appealing to the public for details about Mr Lawrence's personal life, including any conflicts or problems he was involved in.